Computers, such as personal computers, have system clocks that are necessary for proper operation of the computers. From time to time the computer system clock will become out of sync (lose or gain time) due to power failures or frequency drifts, for example. In the prior art it is necessary for the user to become aware that the system clock of the computer is no longer displaying the correct time. Once this has been determined, the user must manually update or reset the computer's clock. This is a drawback in the prior art because, for example, many documents may be created before the user realizes the system clock is not set to the correct time.
Today many computers have television tuners, such as in tuner cards manufactured by ATI Technologies, Inc. The television tuner allows the personal computer to receive real time television signals. As is well known in the art the television signals have even and odd fields that are interlaced in a television receiver to produce an image. A field contains a plurality of lines of information. In one known format lines 1–21 of a field are referred to as the vertical blanking interval, and the remaining lines contain data with regards to an image to be displayed by the television receiver. In the odd field line 21 contains closed caption data, and in line 21 of the even field is stored extended data services information (EDS or XDS). This information includes, for example, parental control information, programming information, channel identification information (station identifier), and time stamp information (current time). For the DTV, HDTV (digital television), the time stamp information is also available in the PSIP (Program and system Information Protocol) digital payload. This information is used by a variety of electronic equipment, such as, televisions, and video recorders, for example. Some of the commercial video recorders will reset the clock from the EDS information, in case of a power failure, but such recorders typically do not have built-in intelligence to verify that the time stamp information is correct for the given geographic region, e.g., it may pick the time stamp from a station that is broadcast from another time zone. However, although such television signals are used to display images on a personal computer display device, it is a drawback of the prior art that the system clocks of personal computers must be manually updated by a user.
Therefore, there is a need in the prior art for a method and apparatus that provide automatic update of the system clock in a personal computer to a correct time. There is a further need in the prior art to ensure that system clock is updated only when the received time stamp information is valid for the time zone in which the computer is physically located.